(1) Field of the Invention
The present invention relates to a method using particles for providing pre-selected amounts of a chemical to a microorganism over time. In particular, the present invention relates to a particle for delivery of a nutrient to a microorganism which is released in small amounts over time from the particle. The method is particularly useful for bioremediation of contaminated sites in situ.
(2) Description of Related Art
There is a need to deliver chemicals over time to a microorganism. The purpose can be to produce a chemical, such as an enzyme, or drug or to facilitate the growth of the microorganism.
Toxic compounds contaminating the environment can be converted into innocuous substances by microbial digestion of the toxic substances, referred to as bioremediation. Bioremediation has been used to treat soil in above-ground treatment systems, above-ground bioreactors, slurry pits, above-ground soil heaps, compositing material, and in subsurface systems in situ.
The current methods for introducing remediation compositions into contaminated environments include injection of liquid or gas phase components into subsurface environments, extraction of liquid or gas phase components and treatment ex situ, or excavation of contaminated sites for treatment ex situ. These methods are labor intensive and expensive. It will become apparent that the prior art does not provide for an inexpensive, versatile and effective means for in situ remediation. The most closely related prior art is as follows.
U.S. Pat. No. 3,224,946 to Raymond relates to the use of zeolites to absorb the hydrocarbons to be degraded and then degrading the hydrocarbon with the microorganism. Specifically, this method uses hydrous aluminosilicate to act as a molecular sieve whereby hydrocarbonaceous material may become lodged until the material is released by chemical conversion by a bacteria. The method provides for an in vitro means for degrading hydrocarbonaceous material ex situ.
U.S. Pat. No. 4,039,438 to Anderson describes the use of pulp or paper as a substrate with bacteria to reduce nitrate in water.
U.S. Pat. No. 5,268,109 to Boyd describes the use of clays which have been ion exchanged to remove contaminants. The method does not relates to in situ remediation.
U.S. Pat. No. 5,265,674 to Frederickson et al relates to the introduction of oils and nutrients and optimally microorganisms into a zone to be remediated. The method effects remediation by pumping liquid oil into a contaminated site and allowing the oil to move throughout the soil concentrating and absorbing the contaminants. The oil containing the contaminants is then removed from the soil. An additional method proves for the addition of microbes to the oil applied to the site and allowing the microbes to degrade the contaminants concentrated by the oil. A limitation of this method is that the oil is applied to the remediation zone in liquid form. In liquid form, the dissolution of the oil is fairly rapid therefore, requiring repeated applications to effectively remove the contaminants.
U.S. Pat. No. 5,299,638 to Cheneviere et al relates to the use of clays or other porous materials with bacteria to produce viscosity promoting polymers.
U.S. Pat. No. 5,340,376 to Cunningham relates to the controlled release of nutrients with a timed release coating. Once the coating is gone, the nutrient is released. The invention provides for remediation by providing nutrients for the bacteria fauna already present which then degrade the contaminating organic compounds. The nutrients are provided as granules of urea coated with a resin which when introduced into a site continuously provide nutrients for up to three months. The limitation of the invention is that it relies on the naturally occurring bacteria fauna already present at the contaminated site. If the site does not provide the bacterial species that are capable of degrading the offending contaminant or in sufficient numbers then the invention will not be effective for remediation. Furthermore, the composition and method were designed for surface level remediation wherein the composition is tilled into the soil.
U.S. Pat. No. 5,348,803 to Schlaemus et al relates to microcapsules of microorganisms and hydrocarbons as nutrients. This invention is an improvement over the previous invention in that capsules having a water insoluble coating containing a microorganism capable of degrading hydrocarbons surrounds a core that provides nutrients for the microorganism. The invention is designed to be sprayed on oil spills in an aqueous environment whereby the microcapsules being water insoluble remain associated with the oil.
U.S. Pat. No. 5,401,413 to Gatt et al relates to microorganisms and exposures for bioremediation. The invention provides a composite material having a core containing water soluble microbial nutrients and a partially oil soluble and biodegradable coating. The composite material is sprayed or dusted onto an oil spill whereby the oil soluble coating causes the composite to associate with the oil contamination.
U.S. Pat. No. 5,602,036 to Criddle et al relates to metabolites of Pseudomonas which enhance bioremediation. Metabolites produced by Pseudomonas are introduced into a material containing a halogenated hydrocarbon and an indigenous or added bacterium to effect degradation of the halogenated hydrocarbon by the bacterium.
U.S. Pat. No. 5,560,737 to Schuring et al relates to pneumatic fracturing and introduction of microorganisms or nutrients into the fracture.
U.S. Pat. No. 5,730,550 to Andersland et al describes the use of a freeze wall for placement of a bioremediation method in situ.
The problem with this prior art is that an effective method for placement of the long term or time (months) released nutrients and/or microorganisms in situ is not described. This limitation and other limitations of the prior art will become more apparent from the discussion that follows.